Project Year 2015

Rested cod best

Consumers want cod that is good enough, the industry is looking for enough cod. Nofima seek to know whether the cod welfare is good enough.

The conclusion so far is that stressed and exhausted newly caught trawl fish can be rested to achieve good quality in the course of six hours.

Ph.D. stipendiary Ragnhild Aven Svalheim has carried out several different trials using a custom-built swimming tunnel at the Aquaculture Station in Tromsø.

The work has dealt with experimental simulation of the conditions that arise during commercial trawl fishing, and investigations into how these conditions affect the fish’s physiology and which impact this has on the quality of the raw material.

The different phases of trawl fishing are physical exhaustion as the fish try to avoid the mouth of the net, crowding when they are gathered in the trawl and lifted out of the water, and major changes in pressure from different depths and up to the surface.

“The swimming tunnel is basically a trawl simulator where we can imitate the different stages of trawl fishing,” Svalheim says.

During high activity swimming, fish are unable to provide their muscles with enough oxygen. The lack of oxygen and use of energy causes the muscle to sour and accumulate lactic acrid. In order to tacle the change in pH and obtain new energy, blood is redistributed to the muscle causing a reddening in the musculature for a few hours while it is resting.

When the white muscles of white fish become red, quality is considered to be deteriorated.

The amount of blood in white muscle increases for 2-4 hours after exertion, before returning to the resting level.

The project Ragnhild Svalheim is working on is a part of CRISP – a centre for research-driven innovation in sustainable fishery.

The results are relevant in connection with trials carried out on trawlers, where one has tested pumping live fish from the net with a subsequent resting period in containers filled with water.

“Fish that are stored alive on board have higher quality than fish that die in reception bins without water. The interesting thing to look at now is how to bring the fish efficiently and carefully onto the vessel. Rested cod maintain the best quality,” the researcher concludes.